Catalyst components for the stereospecific polymerization of olefins are known in the chemicals arts. One catalyst family used for the polymerization of olefins such as propylene belongs to the Ziegler-Natta category which generally comprise a solid catalyst component, magnesium dihalide, a titanium compound and an internal electron donor compound, often used in combination with an Al-alkyl compound. When higher crystallinity of the polymer is required, an external donor (for example, an alkoxysilane) may be needed in order to obtain higher isotacticity. One class of internal donors is the esters of phthalic acid, such as diisobutylphthalate. The phthalates are often used as internal donors in combination with alkylalkoxysilanes as external donor. This catalyst system generally gives good performance in terms of activity, isotacticity and xylene insolubility.
However, the use of this catalyst system with phthalates has recently raised concerns due to potential medical issues associated with their use.
Consequently, alternative classes of internal donors for use in the preparation of catalyst components for propylene polymerization have been investigated.
Some alternative catalysts contain donor structures having simultaneously amide groups and ester groups. For instance, WO2006/110234 describes amino acid derivatives including one carbamate group and one free ester function. However, the catalysts generated by these structures have very low activity and stereospecificity in bulk propylene polymerization (please see Table 2).
Another class of internal donors is described in WO2011/068770, which relates to two atom-bridged dicarbonate compounds. According to this document, good results can be obtained when the diol portion is part of a substituted phenyl group, which show interesting stereospecificity but insufficient activity. Moreover, the document discloses that donors having only one carbonate function such as diethyl carbonate have very low performance.